Commit b504b6aa authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc: differentiate kthread from user kernel thread start 



Kernel created user threads start similarly to kernel threads in that
they call a kernel function after first returning from _switch, so
they share ret_from_kernel_thread for this. Kernel threads never return
from that function though, whereas user threads often do (although some
don't, e.g., IO threads).

Split these startup functions in two, and catch kernel threads that
improperly return from their function. This is intended to make the
complicated code a little bit easier to understand.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230325122904.2375060-7-npiggin@gmail.com
parent eed7c420

arch/powerpc/kernel/entry_32.S

+18 −2
Original line number Diff line number Diff line
@@ -186,8 +186,8 @@ ret_from_fork: 
	li	r3,0	/* fork() return value */

	b	ret_from_syscall



	.globl	ret_from_kernel_thread

ret_from_kernel_thread:

	.globl	ret_from_kernel_user_thread

ret_from_kernel_user_thread:

	bl	schedule_tail

	mtctr	r14

	mr	r3,r15
@@ -196,6 +196,22 @@ ret_from_kernel_thread: 
	li	r3,0

	b	ret_from_syscall



	.globl	start_kernel_thread

start_kernel_thread:

	bl	schedule_tail

	mtctr	r14

	mr	r3,r15

	PPC440EP_ERR42

	bctrl

	/*

	 * This must not return. We actually want to BUG here, not WARN,

	 * because BUG will exit the process which is what the kernel thread

	 * should have done, which may give some hope of continuing.

	 */

100:	trap

	EMIT_BUG_ENTRY 100b,__FILE__,__LINE__,0





/*

 * This routine switches between two different tasks.  The process

 * state of one is saved on its kernel stack.  Then the state

arch/powerpc/kernel/interrupt_64.S

+17 −1
Original line number Diff line number Diff line
@@ -739,7 +739,7 @@ _GLOBAL(ret_from_fork) 
	li	r3,0	/* fork() return value */

	b	.Lsyscall_exit



_GLOBAL(ret_from_kernel_thread)

_GLOBAL(ret_from_kernel_user_thread)

	bl	schedule_tail

	mtctr	r14

	mr	r3,r15
@@ -749,3 +749,19 @@ _GLOBAL(ret_from_kernel_thread) 
	bctrl

	li	r3,0

	b	.Lsyscall_exit



_GLOBAL(start_kernel_thread)

	bl	schedule_tail

	mtctr	r14

	mr	r3,r15

#ifdef CONFIG_PPC64_ELF_ABI_V2

	mr	r12,r14

#endif

	bctrl

	/*

	 * This must not return. We actually want to BUG here, not WARN,

	 * because BUG will exit the process which is what the kernel thread

	 * should have done, which may give some hope of continuing.

	 */

100:	trap

	EMIT_BUG_ENTRY 100b,__FILE__,__LINE__,0

arch/powerpc/kernel/process.c

+4 −3
Original line number Diff line number Diff line
@@ -1741,7 +1741,8 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 
	struct pt_regs *kregs; /* Switch frame regs */

	extern void ret_from_fork(void);

	extern void ret_from_fork_scv(void);

	extern void ret_from_kernel_thread(void);

	extern void ret_from_kernel_user_thread(void);

	extern void start_kernel_thread(void);

	void (*f)(void);

	unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;

	struct thread_info *ti = task_thread_info(p);
@@ -1758,7 +1759,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 
		sp -= STACK_FRAME_MIN_SIZE;

		((unsigned long *)sp)[0] = 0;



		f = ret_from_kernel_thread;

		f = start_kernel_thread;

		p->thread.regs = NULL;	/* no user register state */

		clear_tsk_compat_task(p);

	} else {
@@ -1784,7 +1785,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 
			childregs->softe = IRQS_ENABLED;

#endif

			ti->flags |= _TIF_RESTOREALL;

			f = ret_from_kernel_thread;

			f = ret_from_kernel_user_thread;

		} else {

			struct pt_regs *regs = current_pt_regs();

			unsigned long clone_flags = args->flags;